Concealed by darkness: Combination of NMR and HRMS reveal the molecular nature of dissolved organic matter in fractured-rock groundwater and connected surface waters.

Detailed molecular composition of solid phase extracted dissolved organic matter (SPEDOM) collected from fractured-rock groundwater was compared to connected surface river water at two different watersheds in the unconfined chalk aquifer of Champagne in France using full scan ultrahigh resolution electrospray and photoionization Fourier transform ion cyclotron mass spectrometry (FT-ICR MS), Orbitrap tandem MS (MS/MS) and 1H magnetic resonance spectroscopy (NMR). 1H NMR spectroscopy indicated that groundwater SPEDOM carried a higher contribution of aliphatic compounds while surface river waters SPEDOM were enriched in carboxyl-rich alicyclic molecules (CRAM), acetate derivatives and oxygenated units. Furthermore, we show here that use of photoionization (APPI(+)) in aquifer studies is key, ionizing about eight times more compounds than ESI in surface river water samples, specifically targeting the dissolved organic nitrogen pool, accounting for more than 50% of the total molecular space, as well as a non-polar, more aromatic fraction; with little overlap with compounds detected by ESI(-) FT-ICR MS. On the other hand, groundwater SPEDOM samples did not show similar selectivity as less molecular diversity was observed in APPI compared to ESI. Mass-difference transformation networks (MDiNs) applied to ESI(-) and APPI(+) FT-ICR MS datasets provided an overview of the biogeochemical relationships within the aquifer, revealing chemical diversity and microbial/abiotic reactions. Finally, the combination of ESI(-) FT-ICR MS and detailed Orbitrap MS/MS analysis revealed a pool of polar, anthropogenic sulfur-containing surfactants in the groundwaters, likely originating from agricultural runoff. Overall, our study shows that in this aquifer, groundwater SPEDOM contains a significantly reduced pool of organic compounds compared to surface river waters, possibly related to a combination of lack of sunlight and adsorption of high O/C formulas to mineral surfaces.

Bioactivity of humic substances and water extracts from compost made by ligno-cellulose wastes from biorefinery.

The ligno-cellulose residues from biorefinery production of bio-ethanol were used as woody structuring material within an on-farm composting system, with the aim to obtain bioactive water soluble and humic fractions from composted materials. The molecular characterization of initial biomasses and final products revealed a transformation towards more stable compounds during composting and showed the selective incorporation of specific phenolic derivatives of ligno-cellulose in both bulk samples and corresponding extracts. While the use of the stable bulk composts as organic fertilizer resulted in a decrease of nitrogen and phosphorous assimilation in maize tissues, a bio-stimulation was shown by water soluble organic compounds and humic substances in germination tests and pot experiments, respectively. The differential responses obtained in maize seedlings and plants were related to the molecular composition and concentration of the applied water extracts and humic substances, thus suggesting a role of phenols and lignin derivatives in the stimulation of maize roots and shoots and the enhancement of P uptake. The results confirm that ligno-cellulose residues may be effectively recycled as composting additives in order to enrich mature compost in aromatic and lignin compounds. A preliminary knowledge on the molecular characteristics and biological properties of composted materials is an essential requirement to select the most suitable derivatives from composted ligno-cellulose wastes in sustainable agricultural practices.

Characterization of typical aquatic humic substances in areas of sugarcane cultivation in Brazil using tetramethylammonium hydroxide thermochemolysis.

Aquatic humic substances (AHSs) differ from one environment to another depending on land use and occupation. In addition, the effects of planting sugarcane on AHSs are not well known. Thus, the aim of this study was to characterize AHSs extracted from a river in a typical region of sugarcane cultivation during dry and rainy seasons. The main characteristics of the AHSs were obtained using Fourier transformation infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and off-line pyrolysis coupled with gas chromatography and mass spectrometry (off-line tetramethylammonium hydroxide (TMAH)-GC-MS-thermochemolysis). The FTIR and NMR results were used to infer that no distinctions occurred between the sampling periods. The samples were composed of aromatic groups that were potentially associated with the presence of residual vegetable materials (lignin). The results of the off-line TMAH-GC-MS-thermochemolysis indicated that the structures of the AHSs had uniform compositions that were rich in fatty acid methyl esters (FAMEs), polysaccharide derivatives, aliphatic biopolymers derived from plants, long hydrocarbon chains, branched alkyl groups and methylene carbons. Thus, the results showed that the AHSs obtained from the sugarcane cultivation area during the crop period mainly consisted of resistant aliphatic hydrocarbons, which are derivatives of lignin and FAMEs in compounds rich in humic acid. Therefore, we concluded that sugarcane cultivation produces changes in AHSs because greater amounts of lignin derivatives were observed during the dry season, corresponding to sugarcane cultivation.

Stabilization by hydrophobic protection as a molecular mechanism for organic carbon sequestration in maize-amended rice paddy soils.

The hydrophobic components of soil organic matter (SOM) are reckoned to play an important role in the stabilization of soil organic carbon (SOC). The contribution of hydrophobic substances to SOC sequestration was evaluated in four different paddy soils in the South of China, following a 6-month incubation experiment with maize straw amendments. Soil samples included: a well developed paddy soil (TP) derived from clayey lacustrine deposits in the Tai Lake plain of Jiangsu; an acid clayey paddy soil (RP) derived from red earth in the rolling red soil area of Jiangxi; a weakly developed neutral paddy soil (PP) formed on Jurassic purple shale from Chongq; and a calcic Fluvisol (MS) derived from riverine sediments from a wetland along the Yangtze valley of Anhui, China. The SOC molecular composition after 30 and 180 days of incubation, was determined by off-line thermochemolysis followed by gas chromatography-mass spectrometry analysis. Lignin, lipids and carbohydrates were the predominant thermochemolysis products released from the treated soils. A selective preservation of hydrophobic OM, including lignin and lipids, was shown in maize amended soils with prolonged incubation. The decomposition of lignin and lipids was significantly slower in the TP and RP soils characterized by a larger content of extractable iron oxyhydrates (Fed) and lower pH. The overall increase in hydrophobic substances in maize incubated samples was correlated, positively, with total content of clay and Fed, and, negatively, with soil pH. Moreover, yields of both lignin and lipid components showed a significant relationship with SOC increase after incubation. These findings showed that the larger the lipid and lignin content of SOM, the greater was the stability of SOC, thereby suggesting that OM hydrophobic components may have an essential role in controlling the processes of OC sequestration in paddy soils of South China.

Molecular properties of a fermented manure preparation used as field spray in biodynamic agriculture.

Manure products fermented underground in cow horns and commonly used as field spray (preparation 500) in the biodynamic farming system, were characterized for molecular composition by solid-state nuclear magnetic resonance [(13) C cross-polarization magic-angle-spinning NMR ((13) C-CPMAS-NMR)] spectroscopy and offline tetramethylammonium hydroxide thermochemolysis gas chromatography-mass spectrometry. Both thermochemolysis and NMR spectroscopy revealed a complex molecular structure, with lignin aromatic derivatives, polysaccharides, and alkyl compounds as the predominant components. CPMAS-NMR spectra of biodynamic preparations showed a carbon distribution with an overall low hydrophobic character and significant contribution of lignocellulosic derivatives. The results of thermochemolysis confirmed the characteristic highlighted by NMR spectroscopy, revealing a molecular composition based on alkyl components of plant and microbial origin and the stable incorporation of lignin derivatives. The presence of biolabile components and of undecomposed lignin compounds in the preparation 500 should be accounted to its particularly slow maturation process, as compared to common composting procedures. Our results provide, for the first time, a scientific characterization of an essential product in biodynamic agriculture, and show that biodynamic products appear to be enriched of biolabile components and, therefore, potentially conducive to plant growth stimulation.

Polymerization of humic substances by an enzyme-catalyzed oxidative coupling.

A novel understanding of the structural features of humic substances supports the self-assembly supramolecular association of relatively small molecules rather than their polymeric nature. An increase in the conformational stability of humus may thus be achieved through promotion of intermolecular covalent bondings between heterogeneous humic molecules by an enzyme-catalyzed oxidative reaction. We present evidence from high performance size exclusion chromatography (HPSEC) and diffuse reflectance infrared spectrometry (DRIFT) that oxidation of a humic material catalyzed by horseradish peroxidase stabilizes the humic structure by the formation of aryl and alkyl ethers and permanently enhances its molecular size.

Increased sequestration of organic carbon in soil by hydrophobic protection

The impact of soil organic carbon dynamics on the global carbon cycle is still largely uncertain despite studies of agricultural activities and control emissions of greenhouse gases to the earth's atmosphere. Improved knowledge of organic matter dynamics should lead to reduction in CO(2 )emissions. We used stable carbon isotope analysis to detect small changes in organic carbon storage and turnover upon soil treatments with a (13)C-labeled aliphatic alcohol previously partitioned into soluble humic substances of varying hydrophobicity. We found that labeled organic carbon is increasingly protected from mineralization with increased hydrophobic character of humic matter. The stabilization of organic carbon by hydrophobic protection significantly reduced decomposition during incubation time in soil. Hydrophobic protection can become an useful tool to limit decomposition of fresh organic matter in soil and thus reduce CO(2) emission from agricultural soils on a global scale.http://link. springer.de/link/service/journals/00114/bibs/9086010/90860496. htm